Macronutrients & Organic Carbon

1. Macronutrients & Organic Carbon Micronutrients Silicon Nitrogen Phosphorous Organic Carbon

2. Iron Cycling • Ferrous is most bioavailable for assimilation. • Chemoautotrophic oxidation by acidophilic or neutrophilic iron bacteria. • Precipitation under oxic and phosphorous rich conditions. • Organic carbon chelators prevent precipitation; bioavailability mayincrease with microbial siderophores yet high humic acids may cause limitations. • Ferric can be used for anaerobic respiration by iron reducing bacteria.

3. Silicon • Source is weathering of aluminosilicates! • Extremely low solubility, yet everywhere. • Silica and silicic acid as dissolved forms. • Diatom need it for frustrules; supply limits growth.

4. Nitrogen • Macronutrient; Uptake and Assimilation to Organic-N: • May limit freshwater 1º Production; • Algal autotrophs prefer inorganic-N (NH4+ preferred to NO3-) • Bacteria heterotrophs prefer organic-N (esp. amino acids) • Glutamine Synthetase expressed when N-starved. • Major microbial processes that transform N: • N2-Fixation: N2 to NH4+; needs absence of O2; only bacteria. • Regeneration (remineralization; decomposition): • Organic-N to ammonium (NH4+) and excreted; • N-replete bacteria ≥ protists > zooplankton >> others • Nitrification: 2 different bacterial steps; NH4+ to NO2- to NO3- • Anaerobic NO3- Respiration: NO3- as e- acceptor to NO2-. • Denitrification: NO3- to NO2- to N2O gas to N2 gas; gas to atm.

5. N2O

6. Nitrogen Analysis • Total N: Kjeldahl digestion of all N-forms to NO3-, which gets analyzed (see below). • Particulate N: Filter harvest particles; Dumas combustion followed by GC separation of N2 and thermocoupler detection. • Total Dissolved N (TDN): Filtrate subject to Kjeldahl digestion to NO3-. • Dissolved Inorganic N (DIN) forms: • Ammonium: colorimetric; phenol or salicylate rxn. • Nitrate: Cd/Zn reduction to NO2-(see next). • Nitrite: colorimetric; azo-dye rxn. • Dissolved Organic Nitrogen (DON): = TDN – DIN

7. Phosphorous • Macronutrient; Uptake and Assimilation to Organic-P: • Often limits freshwater 1º Production; • Algal autotrophs and bacterial heterotrophs prefer o-phosphate (PO4-3) over organic-P forms. • Bacteria can be superior competitors for PO4-3. • Alkaline Phosphatase expressed when P-starved. • Sources and Fates: • Weathering of P-containing minerals from soil and rocks. • Ultimately, stores in sediments of lakes and ocean. • Cycling very rapid and often in low concentration. • Total phosphorous is the best measure of available P.

9. Phosphorous Analysis • Particulate and dissolved forms separated by filtration. • Total Phosphorous: heated acid persulfate (ox.) digestion to o-PO4-3. Filtrate yields total dissolved P (TDP). • Acid Hydrolysable P (AHP): o-PO4-3 and condensed (polymerized) phosphates by heated acid hydrolysis to PO4-3. • Ortho-phosphate (o-PO4-3): soluble reactive phophorous (SRP); assay is colorimetric by the ascorbate-molybdate complex rxn. • Dissolved Organic P: DOP = TDP – AHP – SRP

10. Organic Carbon • Measured to approximate system energy flow and biomass. • Sources: • Allochthonous (mostly from the terrestrial environment; plants and soil) • Autochthonous (made within system by autotrophs) • Particulate Forms: • Biomass: living cells and organisms • Detritus: dead fragments of organisms; precipitates of organics • FPOM; CPOM; Large Woody Debris • Dissolved Forms: majority of organic matter! • Labile: reduced; simple; preferred and used rapidly by microbes. • (e.g. carbohydrates, amino acids, lipids, peptides, nucleotides) • Refractory: oxidized; complex; polymeric; degrades slowly. • (e.g. lignin, tannins, humics, other polyphenolics of terrestrial plant origin). • Effects: weak acidic buffer; toxicity (direct indirect); and color.

12. Carbon Cycling

13. Organic Carbon Analysis • Again, dissolved and particulate forms separated by filtration. • Acidification is used to remove carbonates so that analysis is only of organic carbon. • Particulate organic C (POC): Dumas combustion followed by GS separation of CO2 and thermocoupler detection. • Dissolved organic C (DOC): most common now is high temperature platinum catalyst oxidation and IR detection of evolved CO2.

14. Water Color • Apparent Color (unfiltered): • True Color plus …. • Particles • Clay and silt • Phytoplankton • Bottom reflected color (in situ)

15. True Color (filtered sample) • Pale yellow to dark coffee color of DOM • Pale blue of soda lakes (very high carbonate content) • Platinum Cobalt salts as standards

16. Wood-waste Leachate Treatment Wetland UV light and O* free radicals →